Various types of amplifier circuits have been developed for a myriad of applications, such as including audio applications, video applications and communications applications to name a few. Some core considerations for most amplifier designs are the ability to support a wide bandwidth and provide low distortion in the amplified output signal.
In certain circumstances, it is desirable to limit the upper and/or lower bounds of an amplifier output voltage. Consequently, a type of amplifier generally referred to as voltage limiting or clamping amplifier has been developed. Clamping amplifiers are useful to enable a user to protect downstream circuitry, such as from over driving input signals to the amplifier. Thus, clamping amplifiers can be utilized in various amplifier configurations for audio, video and communications applications. Examples of some clamping amplifier circuit configurations include non-inverting gain amplifiers, inverting gain amplifiers, rectifiers, Schmitt triggers, unity gain buffers and pulse generators.
Typical clamping amplifiers enable a user to set high and low clamping voltages for the amplifier output voltage. Thus, by setting the clamping voltages, the output of the amplifier will clamp at the specified levels.
By way of example, one type of clamping amplifier includes first and second amplifier stages. Input pins receive a differential input voltage as well as both high and low clamping voltages. Input buffers isolate the input pins from a pair of comparators and an associated switch. The comparators drive the switch through a decoder to control which buffered input is provided to the non-inverting input of the first gain stage of the amplifier. This type of clamping amplifier configuration generally only works for non-inverting or follower applications. To clamp in an inverting circuit configuration, an additional inverting gain stage would be required. Additionally, since the clamping is implemented at the input of the amplifier, the clamp voltage levels and input error are multiplied by the amplifier's closed loop gain at the output. Consequently, this further requires that calculations be performed in order to set desired clamping levels for the amplifier.
While various other approaches exist for implementing the voltage clamping, improvements in performance for clamping amplifiers are still desired for many applications.